 Mucous membranes –Conjunctiva –Respiratory –Gastrointestinal tract –Urogenital  Skin –Abrasions or bite  Parenteral –Puncture or injection Portals of Entry

Portal of Exit

Stages of Release of Microbes

Pattern of Transmission

Sneeze and Microbe Spread

How Did the Pathogen Leave the Host?  Active escape: Movement of pathogen to portal of exit Movement of pathogen to portal of exit  Passive escape: Excretion in feces, urine, droplets, saliva Excretion in feces, urine, droplets, saliva

Virulence and the Mode of Transmission  Direct contact: Less virulent  Vector-borne: Highly virulent in human host; relatively benign in vector  Greater ability to survive outside host: More virulent

Reduce or eliminate source or reservoir  Isolation of cases and carriers  Destruction of animal reservoir  Treatment of sewage  Therapy that reduces or eliminates infectivity of cases

Break Connection Between Source and Susceptible Individuals  Chlorination of water  Pasteurization of milk  Inspection of food and food handlers  Destruction of insect vectors